Tolerances: Expectations for Industrial 3D Printing

​In the world of additive manufacturing, “What tolerance can you guarantee?” is the question everyone asks -- and the one no responsible shop should ever answer with a promise. Industrial 3D printing doesn’t produce deterministic, CNC‑style outcomes because parts are produced uninterrupted and without room for rework mid-print. The tremendous flexibility and speed that the process affords our customers has its price in that we can’t make promises about precisely how accurate a certain geometry, in XYZ material, will print.  

Furthermore, so many of the shapes that we print are ones that can’t easily be measured; plastics in general are difficult to pin down due to their relatively high coefficient of thermal expansion, flexibility, and in many cases large radii and organic curves that escape the jaws of any caliper or micrometer. 

With that being said, we stand behind the quality of our work and accuracy of our systems.  For starters, POP has chosen our machines carefully, primarily based on their reliability and accuracy.   Furthermore, we inspect 100% of parts for gross defects (missing features, severe warpage, poor cleaning, and other occasional/avoidable defects).  With professional operation and maintenance, Systems like the Stratasys Fortus 900mc, Objet Connex 500, and 3D Systems Projet 7000HD will make parts very repeatability, and enable engineers and designers to set smart, realistic expectations about what dimensional accuracy they'll receive. Think of these not as guarantees, but as rules of thumb that help you design parts that print well and avoid surprises.

FDM (Stratasys Fortus 900mc)
Typical tolerance range: ±0.005 in ± 0.0015 in/in
The Fortus 900mc is the heavyweight champion of FDM: it weighs more than our TRAK CNC mill and makes arguably the best FDM parts possible – certainly the largest!  Its heated chamber, servo‑driven (ballscrew!) axes, and closed-loop extrusion control all but guarantee that the parts that come out of it will be good.  But at the end of the day it’s still FDM, laying down molten polymer bead by bead. That means:

• Holes tend to print undersized (we recommend adding 0.005" radially for a pretty reliable slip fit)
• Corners can soften slightly from thermal rounding, and tiny features aren't recommended for the same reason
• Small seams/extrusion artifacts are normal, and can throw measurements off locally
• Solid, thick parts can show subtle warp (most of the time this is not an issue, but can be depending on material choice)

Design mindset: It's accurate, but not CNC.  If a tight dimension really matters, leave machining stock or plan for a post‑process touch‑up.
 
PolyJet (Stratasys Connex 500)
Typical tolerance range: ±0.004in below 1.5in part size, ±0.008in for larger parts
PolyJet prints a photopolymer resin through inkjet heads, producing parts that are smooth, with crisp features and capable of extreme detail. But even PolyJet has its limits: the material is jetted as a liquid during printing (leading to some loss of accuracy), and the support gel scaffolding that gives parts their matte finish can also affect final part tolerances.  Keep in mind that rubber-like materials generally print with slightly looser tolerances -- and are nearly impossible to measure due to their squishiness. 
Expect:

• Slight swelling and texture on sidewalls (parts tend to measure oversize, with holes undersize)
• Large flat planes can show faint waviness due to jetting lines and/or roller “knock”
• Dimensional drift often increases with part size, primarily due to resin shrinkage and how the machine attempts to compensate for that -- a very geometry dependent process

Design mindset: Treat PolyJet as a precision visual tool, but not necessarily a substitute for machined accuracy

SLA (3D Systems Projet 7000HD)
Typical tolerance range: ±0.002 in ± 0.0015 in/in
If your device is all about print accuracy, industrial (vat) SLA is hard to beat. The Projet 7000HD delivers smooth surfaces, sharp details, and consistent small features. But even the best resin still (slightly) shrinks, curls, and moves as it cures.
Expect:

• Post‑cure warpage is possible for long and/or very thin parts
• Tiny support nubs remain that can affect measurements if not finished

Design mindset: Keep walls uniform and design as you would for injection molding
 
In summary: Even with top-notch industrial machines, additive manufacturing is not a deterministic process.  After our visual inspection, parts are sold as‑is, and tolerances are statistical, not contractual.
But when you design with the right expectations, you get robust parts that consistently meet your needs and function as expected:

• FDM: ±0.005 in ± 0.0015 in/in
• PolyJet: ±0.004 to ±0.008 in
• SLA: ±0.002 in ± 0.0015 in/in

These aren’t promises—they’re professional guardrails. And when you stay within them, industrial 3D printing becomes a powerful, predictable tool in your product development arsenal.